New study shows impact of 12,000 years of sea level rises on Isles of Scilly

The Lyonesse Project, a study of the impact of sea level rise on the Isles of Scilly over the past 12,000 years, has been formally published by Cornwall Council with funding from Historic England – marking the culmination of seven years of work.

Popularly associated with the legendary lost land of Lyonesse, the Isles of Scilly were one large island 9,000 years ago. Lyonesse, said to have extended westwards from Land’s End to the Isles of Scilly, was reported to had ‘fair-sized towns and 140 churches’ before being engulfed by the sea. Since the mid-eighteenth century stone walls and other archaeological remains have been identified below high water in Scilly, the result of low-lying land being submerged by the gradual rise in sea-level.

The timing and nature of the changing land areas and the separation of the individual islands has, however, been the subject of much conjecture and debate and research including that by the late Professor Charles Thomas whose classic book ‘Exploration of a Drowned Landscape’ first stimulated serious discussion.

The Lyonesse Project was commissioned by Historic England following the discovery of a submerged forest in St. Mary’s Road by local diver Todd Stevens. The Project was carried out between 2009 and 2013 by the Cornwall Archaeological Unit, part of Cornwall Council, with a team of experts from Aberystwyth, Cardiff, Exeter, Plymouth, Oxford and Glasgow Universities and Historic England’s Scientific Dating Team. Volunteers and local experts from the Cornwall and Isles of Scilly Maritime Archaeological Society and the Islands Maritime Archaeology Group were also involved.

The aim of the project was to reconstruct the evolution of the physical environment of Scilly during the Holocene (11,700 cal BP to present), investigate the progressive occupation of this changing coastal landscape by early peoples, explore past and present climate change and sea-level rise and develop geophysical techniques for mapping submerged palaeolandscapes. The team also aimed to improve management, promote better understanding of the islands’ historic environment and encourage local community engagement with the historic environment.

Analysis of samples of peat and pollen recovered from a range of sites during the project, including beaches and the submerged forest, have provided a unique insight into the development of the landscape through the Holocene epoch, set against the backdrop of changing sea levels.

“The new data shows that the 500-year period between 2500 and 2000 BC saw the most rapid loss of land at any time in the history of Scilly — equivalent to losing two-thirds of the entire modern area of the islands“ said Charlie Johns, Archaeology Projects Officer, Cornwall Archaeological Unit.

“After this the rate of change slowed significantly so that by circa 1500 BC the pattern of islands was approaching that of today, but with the dramatic difference of a vast intertidal area of saltmarsh in what is now the islands’ inner lagoon.

“Much of this would have remained useful land, especially for grazing animal stock and would have been passable with ease almost all of the time. It was not until there was an open channel north of St Mary’s during most states of the tide that the saltmarsh began to erode rapidly: radiocarbon dates suggest this is likely to have occurred in the early medieval period, after 600-670 AD“ he added.

Daniel Ratcliffe, Inspector of Ancient Monuments for Historic England in the South West, said “Historic England is very pleased to have funded this ground breaking research. Our understanding of the internationally important archaeological heritage of Scilly, is fundamentally bound up in our understanding of environmental change. This new cutting edge research will be instrumental in refining our knowledge of how Scilly’s populations have responded to the ever present challenges of living within an evolving coastline throughout history.”

The Lyonesse Project: a study of the historic coastal and marine environment of the Isles of Scilly by Dan J. Charman, Charles Johns, Kevin Camidge, Peter Marshall, Steve Mills, Jacqui Mulville, Helen M. Roberts and Todd Stevens was published by Cornwall Council at the end of July.